1. Field of Invention
The present invention relates to a method of mounting an electric component on a printed-wiring board and particularly to the art of correcting, according to a dimensional error and/or a positional error of the printed-wiring board, a mounting position where the electric component is to be mounted.
2. Related Art Statement
A plurality of ideal mounting positions where respective electric components (xe2x80x9cECsxe2x80x9d) are to be mounted on an ideal printed-wiring board (xe2x80x9cPWBxe2x80x9d) having no dimensional errors or no positional errors, are determined in advance and are pre-stored in a memory. However, before ECs are mounted on an actual PWB, the actual PWB may have at least one dimensional error and/or at least one positional error, for example, because the PWB is produced with at least one erroneous dimension, because the PWB is deformed due to heat or external force applied thereto, and/or because the PWB is erroneously positioned relative to an EC mounting device which is for mounting the ECs on the PWB. In this case, the ideal mounting positions should be modified. The actual PWB has an electrically conductive pattern (e.g., land or pad) at a mounting position where each EC is to be mounted. If the actual PWB has a dimensional error and/or a positional error, the conductive pattern thereof should also have a positional error. If each of the ideal mounting positions is not modified or corrected according to the positional error and/or positional error of the PWB, the electrodes of each EC may not correctly placed on the conductive pattern of the PWB. Japanese Patent Publication No. 8-236997 discloses a method of correcting an ideal EC-mount position according to a dimensional error of a PWB. This conventional method includes (a) calculating a first reference straight line which passes through an ideal EC-mount position and divides, in a first division ratio, each of a first pair of opposed sides of an ideal quadrilateral defined by respective ideal position of four reference points, and a second reference straight line which passes through the ideal EC-mount position and divides, in a second division ratio, each of a second pair of opposed sides of the quadrilateral, and (b) determining, based on the first and second division ratios for dividing the four sides of the ideal quadrilateral, and respective detected actual positions of the four reference points on an actual PWB, an actual EC-mount position where an EC is to be mounted on the actual PWB. Thus, the electrodes of the EC are correctly placed on a conductive pattern of the PWB.
However, the calculations needed for determining the two reference straight lines which divide, in the first and second division ratios, the four sides of the ideal quadrilateral are very complex, which leads to increasing a time needed for processing all the ideal EC-mount positions predetermined for each PWB.
The present invention provides an actual-mounting-position determining method, an electric-component mounting apparatus, an actual-mounting-position determining apparatus, and a mounting-position-correcting-program recording medium which have one or more of the following technical features that are described in below in respective paragraphs given parenthesized sequential numbers (1) to (9). Any technical feature which includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, but not all) of those items.
(1) According to a first feature of the present invention, there is provided a method of determining, according to at least one of at least one dimensional error and at least one positional error of an actual printed-wiring board, an actual mounting position where an actual electric component is to be mounted on the actual board, on a two-dimensional coordinate system defined by a first axis and a second axis, the method comprising the steps of obtaining an ideal relative position of an ideal mounting position which corresponds to the actual mounting position and where an ideal electric component which corresponds to the actual electric component is to be mounted on an ideal printed-wiring board which corresponds to the actual printed-wiring board and which has no dimensional error and no positional error, the ideal relative position being defined as a position of the ideal mounting position relative to four ideal reference-point positions as respective ideal positions of four ideal reference points predetermined on the ideal printed-wiring board, and being defined by four division ratios in which four ideal sides of an ideal quadrilateral defined by the four ideal reference-point positions are respectively divided by two first ideal division points where a first ideal reference line which is parallel to the first axis of the two-dimensional coordinate system and passes through the ideal mounting position intersects a first pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, and two second ideal division points where a second ideal reference line which is parallel to the second axis of the coordinate system and passes through the ideal mounting position intersects a second pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, detecting four actual reference-point positions as respective actual positions of four actual reference points which correspond to the four ideal reference points, respectively, and which are predetermined on the actual printed-wiring board on which the actual electric component is to be mounted, calculating, based on the four division ratios and the four actual reference-point positions, four actual division-point positions as respective actual positions of four actual division points which respectively divide, in the four division ratios, four actual sides of an actual quadrilateral defined by the four actual reference-point positions, and calculating, as the actual mounting position, a position of an intersecting point where a first actual reference line which passes through two first actual division points of the four actual division points that correspond to the two first ideal division points, intersects a second actual reference line which passes through two second actual division points of the four actual division points that correspond to the two second ideal division points.
In the present method, the two ideal reference lines are employed which are independent of the four ideal reference-point positions, and the four division ratios in which the four sides of the ideal quadrilateral defined by the four ideal reference-point positions are divided by the four intersecting or division points where the two ideal reference lines intersect the four sides of the ideal quadrilateral, are determined. Those calculations are much simpler than those of the above-explained conventional method. In addition, since the two ideal reference lines are parallel to the first and second axes of the coordinate system, at least one of the x and y coordinates of each of the four intersecting points of the two ideal reference lines and the four sides is equal to a corresponding one of the x and y coordinates of the ideal mounting position. Because of this, the other of the x and y coordinates of the each of the four intersecting points can be easily determined. Each of the four ideal or actual division ratios may be an xe2x80x9cinsidexe2x80x9d or xe2x80x9coutsidexe2x80x9d division ratio. For example, irrespective of whether the ideal mounting position may be located inside or outside the ideal quadrilateral, four division ratios can be similarly determined and, based on the four division ratios and the detected four actual reference-point positions, four actual division points can be calculated, and the intersecting point of the two actual reference lines can be determined as the actual mounting position. However, in the case where the ideal mounting position is located outside the ideal quadrilateral, one or more of the four sides of the ideal quadrilateral may be extended to find one or more intersecting points where one or more ideal reference lines intersect the one or more sides of the ideal quadrilateral. Here, an xe2x80x9cinsidexe2x80x9d division ratio may be (a1) an internal-division ratio as the ratio of the length of one of two inside segments obtained by dividing one side of an ideal quadrilateral at an inside division point between the two ideal reference points defining the one side, to the length of the other inside segment, or (a2) an inside-segment ratio as the ratio of the length of one of the two inside segments to the entire length of the one side. In the case where an ideal division point is an outside division point located on an extended portion of one side, an xe2x80x9coutsidexe2x80x9d division ratio may be (b1) an external-division ratio as the ratio of the distance between the outside division point and one of the two ideal reference points defining the one side, to the distance between the outside division point and the other ideal reference point, or (b2) an outside-segment ratio as the ratio of the distance between the outside division point and one of the two ideal reference points defining the one side, to the entire length of the one side. The four division ratios as the ideal relative position of one ideal mounting position, or each of a plurality of ideal mounting positions, may be calculated in advance and pre-stored in a memory, so that the four division ratios may be read from the memory, when needed. Alternatively, each time four division ratios are needed, the four division ratios may be calculated based on the ideal mounting position and the four ideal fiducial-mark positions. Otherwise, four division points which are calculated for a certain mounting position on a first or initial PWB, may be stored in a memory, so that the four division points may be read from the memory when an EC is mounted on the corresponding mounting position on each of the second and following PWBs.
(2) According to a second feature of the present invention that includes the first feature (1), the step of calculating the actual mounting position comprises calculating, as at least one correction amount, at least one amount of deviation of the actual mounting position from the ideal mounting position, so that at least one of the actual electric component and the actual printed-wiring board is displaced relative to the other of the actual electric component and the actual board by the correction amount before the actual electric component is mounted on the actual board.
When the thus calculated correction amount is added to the ideal mounting position, and/or a prescribed amount of movement of an EC mounting head, which is or are determined in advance and incorporated into an EC mounting program, the EC can be accurately mounted on a conductive pattern provided on the PWB.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the step of calculating the actual mounting position comprises calculating, based on at least one of respective angular deviations of respective slopes of the first and second actual reference lines from respective slopes of the first and second ideal reference lines, an angular correction amount as an amount of deviation of an actual angular position of the actual printed-wiring board from an ideal angular position of the ideal printed-wiring board about an axis line perpendicular to an upper surface of the actual board, so that at least one of the actual electric component and the actual board is rotated about the axis line by the angular correction amount before the actual electric component is mounted on the actual board.
In the case where the present method calculates the angular correction amount in addition to a positional correction amount, the actual mounting position more accurately reflects, and accommodates, the dimensional and/or positional errors of the actual PWB. The angular correction amount may be determined based on an angular deviation of the slope of a pre-selected one of the two actual reference lines from that of a corresponding one of the two ideal reference lines, or based on respective angular deviations of the respective slopes of the two actual reference lines from those of the corresponding ideal reference lines.
(4) According to a fourth feature of the present invention that includes the third feature (3), the step of calculating the angular correction amount comprises calculating the angular correction amount as an average of the respective angular deviations of the respective slopes of the first and second actual reference lines from the respective slopes of the first and second ideal reference lines.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the step of detecting the four actual reference-point positions comprises detecting respective amounts of positional deviations of the four actual reference-point positions from the four ideal reference-point positions in each of a first direction and a second direction which are parallel to the first and second axes of the two-dimensional coordinate system, respectively, and detecting the four actual reference-point positions as respective sums of the four ideal reference-point positions and the respective amounts of positional deviations of the four actual reference-point positions.
Alternatively, the four actual reference-point positions may be detected or recognized as respective of combinations of coordinates, e.g., respective sets of x and y coordinates.
(6) According to a sixth feature of the present invention, there is provided an electric-component mounting apparatus comprising a mounting device which mounts at least one actual electric component at least one actual mounting position on an actual printed-wiring board having at least one of at least one dimensional error and at least one positional error; control device which controls the mounting device to mount, on a two-dimensional coordinate system defined by a first axis and a second axis, the actual electric component at the actual mounting position on the actual printed-wiring board; and an image taking device which takes an image of the actual printed-wiring board, the control device comprising an ideal-relative-position obtaining portion which obtains an ideal relative position of an ideal mounting position which corresponds to the actual mounting position and where an ideal electric component which corresponds to the actual electric component is to be mounted on an ideal printed-wiring board which corresponds to the actual printed-wiring board and which has no dimensional error and no positional error, the ideal relative position being defined as a position of the ideal mounting position relative to four ideal reference-point positions as respective ideal positions of four ideal reference points predetermined on the ideal printed-wiring board, and being defined by four division ratios in which four ideal sides of an ideal quadrilateral defined by the four ideal reference-point positions are respectively divided by two first ideal division points where a first ideal reference line which is parallel to the first axis of the two-dimensional coordinate system and passes through the ideal mounting position intersects a first pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, and two second ideal division points where a second ideal reference line which is parallel to the second axis of the coordinate system and passes through the ideal mounting position intersects a second pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, an actual-reference-point-position detecting portion which detects, based on image information representing the image of the actual printed-wiring board taken by the image taking device, four actual reference-point positions as respective actual positions of four actual reference points which correspond to the four ideal reference points, respectively, and which are predetermined on the actual printed-wiring board on which the actual electric component is to be mounted, an actual-division-point-position calculating portion which calculates, based on the four division ratios and the four actual reference-point positions, four actual division-point positions as respective actual positions of four actual division points which respectively divide, in the four division ratios, four actual sides of an actual quadrilateral defined by the four actual reference-point positions, and an actual-mounting-position calculating portion which calculates, as the actual mounting position, a position of an intersecting point where a first actual reference line which passes through two first actual division points of the four actual division points that correspond to the two first ideal division points, intersects a second actual reference line which passes through two second actual division points of the four actual division points that correspond to the two second ideal division points.
The present EC mounting apparatus can employ at least one of the second to fifth features (2) to (5).
(7) According to a seventh feature of the present invention, there is provided an apparatus for determining, according to at least one of at least one dimensional error and at least one positional error of an actual printed-wiring board, an actual mounting position where an actual electric component is to be mounted on the actual board, on a two-dimensional coordinate system defined by a first axis and a second axis, the apparatus comprising an ideal-relative-position obtaining means for obtaining an ideal relative position of an ideal mounting position which corresponds to the actual mounting position and where an ideal electric component which corresponds to the actual electric component is to be mounted on an ideal printed-wiring board which corresponds to the actual printed-wiring board and which has no dimensional error and no positional error, the ideal relative position being defined as a position of the ideal mounting position relative to four ideal reference-point positions as respective ideal positions of four ideal reference points predetermined on the ideal printed-wiring board, and being defined by four division ratios in which four ideal sides of an ideal quadrilateral defined by the four ideal reference-point positions are respectively divided by two first ideal division points where a first ideal reference line which is parallel to the first axis of the two-dimensional coordinate system and passes through the ideal mounting position intersects a first pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, and two second ideal division points where a second ideal reference line which is parallel to the second axis of the coordinate system and passes through the ideal mounting position intersects a second pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral; an actual-reference-point-position detecting means for detecting four actual reference-point positions as respective actual positions of four actual reference points which correspond to the four ideal reference points, respectively, and which are predetermined on the actual printed-wiring board on which the actual electric component is to be mounted; an actual-division-point-position calculating means for calculating, based on the four division ratios and the four actual reference-point positions, four actual division-point positions as respective actual positions of four actual division points which respectively divide, in the four division ratios, four actual sides of an actual quadrilateral defined by the four actual reference-point positions; and an actual-mounting-position calculating means for calculating, as the actual mounting position, a position of an intersecting point where a first actual reference line which passes through a first pair of actual division points of the four actual division points that correspond to the two ideal division points, intersects a second actual reference line which passes through two second actual division points of the four actual division points that correspond to the two second ideal division points.
(8) According to an eighth feature of the present invention, there is provided an apparatus for determining, according to at least one of at least one dimensional error and at least one positional error of an actual printed-wiring board, an actual mounting position where an actual electric component is to be mounted on the actual board, on a two-dimensional coordinate system defined by a first axis and a second axis, the apparatus comprising an image taking device which takes an image of the actual printed-wiring board; an ideal-relative-position obtaining means for obtaining an ideal relative position of an ideal mounting position which corresponds to the actual mounting position and where an ideal electric component which corresponds to the actual electric component is to be mounted on an ideal printed-wiring board which corresponds to the actual printed-wiring board and which has no dimensional error and no positional error, the ideal relative position being defined as a position of the ideal mounting position relative to four ideal reference-point positions as respective ideal positions of four ideal reference points predetermined on the ideal printed-wiring board, and being defined by four division ratios in which four ideal sides of an ideal quadrilateral defined by the four ideal reference-point positions are respectively divided by two first ideal division points where a first ideal reference line which is parallel to the first axis of the two-dimensional coordinate system and passes through the ideal mounting position intersects a first pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, and two second ideal division points where a second ideal reference line which is parallel to the second axis of the coordinate system and passes through the ideal mounting position intersects a second pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral; an actual-reference-point-position detecting means for detecting, based on image information representing the image of the actual printed-wiring board taken by the image taking device, four actual reference-point positions as respective actual positions of four actual reference points which correspond to the four ideal reference points, respectively, and which are predetermined on the actual printed-wiring board on which the actual electric component is to be mounted; an actual-division-point-position calculating means for calculating, based on the four division ratios and the four actual reference-point positions, four actual division-point positions as respective actual positions of four actual division points which respectively divide, in the four division ratios, four actual sides of an actual quadrilateral defined by the four actual reference-point positions; and an actual-mounting-position calculating means for calculating, as the actual mounting position, a position of an intersecting point where a first actual reference line which passes through a first pair of actual division points of the four actual division points that correspond to the two ideal division points, intersects a second actual reference line which passes through two second actual division points of the four actual division points that correspond to the two second ideal division points.
(9) According to a ninth feature of the present invention, there is provided a recording medium on which a mounting-position correcting program is recorded such that the program is readable by a computer to determine, according to at least one of at least one dimensional error and at least one positional error of an actual printed-wiring board, an actual mounting position where an actual electric component is to be mounted on the actual board, on a two-dimensional coordinate system defined by a first axis and a second axis, the program comprising the steps of obtaining an ideal relative position of an ideal mounting position which corresponds to the actual mounting position and where an ideal electric component which corresponds to the actual electric component is to be mounted on an ideal printed-wiring board which corresponds to the actual printed-wiring board and which has no dimensional error and no positional error, the ideal relative position being defined as a position of the ideal mounting position relative to four ideal reference-point positions as respective ideal positions of four ideal reference points predetermined on the ideal printed-wiring board, and being defined by four division ratios in which four ideal sides of an ideal quadrilateral defined by the four ideal reference-point positions are respectively divided by two first ideal division points where a first ideal reference line which is parallel to the first axis of the two-dimensional coordinate system and passes through the ideal mounting position intersects a first pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, and two second ideal division points where a second ideal reference line which is parallel to the second axis of the coordinate system and passes through the ideal mounting position intersects a second pair of opposed ideal sides of the four ideal sides of the ideal quadrilateral, detecting four actual reference-point positions as respective actual positions of four actual reference points which correspond to the four ideal reference points, respectively, and which are predetermined on the actual printed-wiring board on which the actual electric component is to be mounted, calculating, based on the four division ratios and the four actual reference-point positions, four actual division-point positions as respective actual positions of four actual division points which respectively divide, in the four division ratios, four actual sides of an actual quadrilateral defined by the four actual reference-point positions, and calculating, as the actual mounting position, a position of an intersecting point where a first actual reference line which passes through two first actual division points of the four actual division points that correspond to the two first ideal division points, intersects a second actual reference line which passes through two second actual division points of the four actual division points that correspond to the two second ideal division points.
The mounting-position correcting program recorded on the present recording medium can employ at least one of the second to fifth features (2) to (5).